The present invention relates to volume adjustable manual pipettes and, more particularly, to an improved manual pipette including a quickly settable volume adjustment mechanism.
U.S. Pat. No. 3,827,305 describes one of the earliest commercially available digitally adjustable air displacement pipettes. To provide for volume adjustment, the pipette includes a threaded shaft extending through a fixed nut. Manual turning of the shaft produces axial movement of a stop member for limiting axial movement of a plunger to define a volume setting for the pipette. The volume setting is displayed on a mechanical micrometer display comprising a series of indicator rings each encircling the threaded shaft.
U.S. Pat. No. 4,909,991 describes a later commercially available single channel manual pipette manufactured by Nichiryo Co. Ltd., Tokyo, Japan. The Nichiryo pipette includes an elongated hand-holdable housing for an upwardly spring biased plunger. An upper end of the plunger extends above a top of the housing and carries a control knob for thumb and finger engagement in manually turning the plunger and for axially moving the plunger in the pipette housing between an upper stop and a lower stop at which all liquid within a tip secured to a lower end of the housing is expelled by the downward movement of the plunger. The upper stop is axially adjustable within the housing in response to a turning of a hollow volume adjustment screw or shaft keyed to the plunger. The axial adjustment of the upper stop adjusts the volume of liquid that the pipette is capable of drawing into the tip in response to upward movement of the plunger to the upper stop. The pipette also includes a lock mechanism including a lock knob for locking the plunger against rotation to thereby set the upper stop in a fixed position and hence set the volume adjustment for the pipette.
Volume adjustable manual pipettes with electronic digital displays have also been developed and are disclosed in U.S. Pat. Nos. 4,567,780; 4,763,535; and 5,892,161.
For a more complete understanding of the current state of the art relative to the volume adjustability of manual pipettes, each of the above-identified patents is incorporated by reference into this application.
In each of the foregoing prior manual pipettes, volume setting requires the repeated turning of either the threaded volume setting shaft or the turning of the displacement plunger of the pipette while viewing the volume display of the pipette. Where successive volume setting for a pipette are of values of considerable difference, appreciable time and physical effort are required to accomplish the volume settings.
Thus, one of the shortcomings of prior manual pipettes is the time, physical effort and care required to accurately manually set the volume of such pipettes. In an attempt to reduce the time required to change the volume settings of a manual pipette, the Socorex Micropipette Calibra 822 includes a volume setting mechanism including two cylindrical cams. A larger one of the cams shows numbers on a left side of a window of a mechanical volume display for the pipette while a smaller one of the cams shows numbers on a right side of the window. After locking of a plunger-button of the pipette, a turning of a setting wheel turns the larger cam to change the numbers displayed thereby. Then a pulling out of the setting wheel followed by a turning thereof produces a turning of the smaller cam and numbers displayed thereby. Such turning of the cams sets mechanical stops within the pipette to control the volume of liquid, which the pipette will aspirate and dispense. While the volume setting structure of the Calibra pipette may reduce the time required to set the volume of a manual pipette, the volume setting structure is relatively complex and costly when compared to conventional manual pipette volume setting mechanisms as described above. Also, the volume setting provided by the Calibra pipette is not as fine a setting as is provided by conventional volume setting mechanisms.
U.S. Pat. No. 6,428,750 issued Aug. 6, 2002 to the assignee of the present invention, describes an improved volume adjustable manual pipette having a quick set volume adjustment that addresses the shortcomings of the Calibra pipette. Basically, that volume adjustable manual pipette comprises an axially elongated hand-holdable housing supporting (i) an electronic digital display and associated position sensing and control circuitry, (ii) a plunger unit and (iii) a quick set volume adjustment mechanism for simultaneously controlling the volume setting of the pipette and the electronic display. The quick set volume adjustment mechanism comprises a pipette volume setting member for limiting upward movement of the plunger unit within the housing to define the volume setting for the pipette. The volume setting member is supported for axial movement on the plunger unit and is releasably secured relative to the housing by a pipette user operable locking mechanism. When released from the housing, the volume setting member is axially moveable on and with the plunger unit to quickly set the volume for the pipette. When secured to the housing, the plunger unit is axially moveable relative to the volume setting unit to aspirate and dispense the selected volume of liquid into and from a pipette tip secured to a hollow shaft extending from a lower end of the housing. The volume setting of the pipette is monitored by the sensing and control circuitry to provide a real time display of the volume setting of the pipette on the electronic digital display. While the quick set features represented a considerable advance in the art of manual pipettes, the multiple step locking and unlocking operation limits the ease and speed of operation of the pipette.
Accordingly, there is a continuing need for a volume adjustable manual pipette including a simple volume adjustment mechanism characterized by quick and highly accurate adjustability. The present invention satisfies that need.